A modern lithifying biofilm, associated with fluvial calcareous tufa in southern Italy, is composed of a complex community of micro-organisms including autotrophic and heterotrophic bacteria, together with likely viruses (bacteriophages) and bacterial vesicles. Produced by most of the bacterial forms, extracellular polymeric substances are widespread and are the main sites of mineral precipitation, rather than the microbial cells themselves, but viruses and vesicles also appear to be mineralized. Neoformed biominerals replace these organic substrates starting with an amorphous phase rich in Ca, Si and several other cations followed by two different types of proto-crystal: a granular−irregular Ca-rich type and a lamellar/fibrous Si-Al-Mg-rich type. Their growth leads to the formation of Ca-carbonate and Mg-silicate crystals that preserve their initial different habits. The coeval precipitation of silicate and carbonate at the initial stage of bio-mediated mineral formation is a process common within freshwater and saline to hypersaline-water calcareous microbialites. This is most probably related to the initial formation of poorly-crystallized Mg-Si phases that precipitate within the extracellular polymeric substances, related to the rise of pH in the zone of active oxygenic photosynthesis, and the mineralization of viruses, associated with the successive nucleation of Ca-carbonate in close proximity to bacterial degradation of organic matter.

中文翻译：

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现代钙质凝灰岩的生物矿化过程：病毒、囊泡和细胞外聚合物的可能作用（Corvino Valley - 意大利南部）

与意大利南部河流钙质凝灰岩相关的现代岩石化生物膜由复杂的微生物群落组成，包括自养和异养细菌，以及可能的病毒（噬菌体）和细菌囊泡。由大多数细菌形式产生的细胞外聚合物广泛分布，是矿物沉淀的主要场所，而不是微生物细胞本身，但病毒和囊泡似乎也被矿化。新形成的生物矿物取代了这些有机底物，从富含钙、硅和其他几种阳离子的无定形相开始，然后是两种不同类型的原晶体：颗粒状-不规则的富含钙的类型和层状/纤维状的富含硅-铝-镁类型。它们的生长导致形成碳酸钙和硅酸镁晶体，这些晶体保持了它们最初的不同习性。在生物介导矿物形成的初始阶段，硅酸盐和碳酸盐的同时沉淀是淡水和盐水到高盐水钙质微生物岩中常见的过程。这很可能与最初形成的结晶不良的 Mg-Si 相在细胞外聚合物中沉淀有关，这与活性氧光合作用区域中 pH 值的升高和病毒的矿化有关，与连续成核有关碳酸钙与有机物质的细菌降解非常接近。在生物介导矿物形成的初始阶段，硅酸盐和碳酸盐的同时沉淀是淡水和盐水到高盐水钙质微生物岩中常见的过程。这很可能与最初形成的结晶不良的 Mg-Si 相在细胞外聚合物中沉淀有关，这与活性氧光合作用区域中 pH 值的升高和病毒的矿化有关，与连续成核有关碳酸钙与有机物质的细菌降解非常接近。在生物介导矿物形成的初始阶段，硅酸盐和碳酸盐的同时沉淀是淡水和盐水到高盐水钙质微生物岩中常见的过程。这很可能与最初形成的结晶不良的 Mg-Si 相在细胞外聚合物中沉淀有关，这与活性氧光合作用区域中 pH 值的升高和病毒的矿化有关，与连续成核有关碳酸钙与有机物质的细菌降解非常接近。